Disclosed herein is a diagnostic module configured to determine an average image of a set or a sequence of collected images, to obtain a last image of the set or the sequence of collected images, and to determine a difference between the average image and the last image to yield a differenced image. Background image data or background pixels are eliminated from the differenced image to produce an initial image mask of unchanged content in the last image. A diagnostic module or data processor determines a mask area of the initial image mask or a revised image mask derived from the initial image mask. A diagnostic module or data processor generates an alert data message to inspect or clean the imaging system if the mask area exceeds a threshold area.
